I could be wrong about this, but I believe plugin_host is running all of the plugins you have installed. So it's possible a plugin is leaking memory. Of course, that's just a guess. Try running ST without any additional plugins and see if the issue persists. You may also want to selectively disable plugins to see if one of them is causing the issue.

@jbrooksuk: I have numerous plugins installed. The one that consistently leaks memory is the SFTP client, and I've notified the author, but he doesn't see the same behavior.

I did just find something that may be meaningful - I've disabled all my packages, and when I open a folder, I can see 60+ Hard Faults/sec being issued from the sublime_text.exe. If I close ST and re-open it without opening a folder, the CPU stays nice, and the memory doesn't leak and the hard faults stay at <10/sec.